In most of the image-guided procedures, after registration, tracked surgical instruments are co-displayed with the previously acquired medical images. Such display visualization of an instrument position in respect to a patient coordinate system has shown to be beneficial for various clinical procedures, particularly procedures involving intra-operative confirmation of the position of the surgical instrument in relation to critical anatomical structures.
Tracking of the surgical instruments (e.g., tissue resection devices, ultrasound transducers, needles, etc.) may be enabled by external position measurement systems (e.g., an optical position measurement system, electromagnetic position measurement system, etc.). In case of robotic surgical tools, tracking with electromagnetic sensors has proven to be impracticable in view of an accuracy of electromagnetic tracking is susceptible to ferromagnetic materials, which are not only present in the operating room but are also commonly used in surgical robotic systems (e.g., stainless steel instruments and robotic arms, electrical motors, etc.).
On the other hand, both high accuracy and ease of integration of optical tracking has made optical tracking technology very popular among the technical community. The most common method is to use external markers that are attached to the arm of the robot. For example, retro-reflective markers in conjunction with an infrared optical tracking system have been used to detect the motion of the robotic arm and reduce Cartesian position error of the robot. Optical tracking using retroreflective markers has also been investigated for minimally invasive robot-assisted pedicle screw placement as well as spinal fusion, where optical marker are mounted on both the robot end-effector and patient's vertebras and used later on for navigation. Another patient-to-robot registration method has been incorporated into a robotic system described where the method involves a coarse registration using point-based matching, and a fine alignment based on the surface matching.